1. You have posted your question in the wrong section. Kindly ensure that you READ WHAT EACH SECTION IS FOR before posting.
2. By USB Drive you mean Hard Disc ?
well, all models come with AC adaptor if they are large Desktop HDDs. If you don't want that, then go for Laptop HDDs. But laptop HDDs are generally not available in 500GB, so you need to buy a case(Rs. 200) + a Laptop HDD of 500GB and insert the disc into the case.